Field of the Invention
Devices for displaying information are being widely developed. The display devices include liquid crystal display (LCD) devices, organic light-emitting display (OLED) devices, electrophoresis display devices, field emission display (FED) devices, and plasma display devices.
Discussion of the Related Art
Among these display devices, OLED devices have the features of lower power consumption, wider viewing angle, lighter weight and higher brightness compared to LCD devices. As such, the OLED device is considered to be next generation display devices.
Thin film transistors used in the organic light-emitting display device can be driven in high speed. To this end, the thin film transistors increase carrier mobility using a semiconductor layer, which is formed from polysilicon. Polysilicon can be derived from amorphous silicon through a crystallizing process.
A laser scanning mode is widely used in the crystallizing process. During such a crystallizing process, the power of a laser beam can be unstable. As such, the thin film transistors formed on the scanned line, which is scanned by the laser beam, can have different threshold voltages from each other. This can cause image quality to be non-uniform between pixel regions.
To address this matter, a technology detecting the threshold voltages of pixel regions and compensating for the threshold voltages of thin film transistors had been proposed.
However, in order to realize such threshold voltage compensation, not only a transistor for detecting the threshold voltage must be added into the pixel region but also signal lines used for controlling the thin film transistors must be added. Due to this, the pixel region becomes complex, and furthermore an aperture of the pixel region decreases.